I started writing CFML in Homesite over a decade ago, and continued using it until CFEclipse finally lured me away last year. Recent changes (i.e. the unfortunate decision to update my Eclipse install into something that now tosses Exceptions out like candies in a parade, no matter how many times I wipe the slate clean and reinstall) has more or less pushed me into using ColdFusion Builder as my full-time IDE. I'm supposedly switching to my Mac soon (I've been saying that since April), so I may switch back once there, but for now I am pushing through with CF Builder.
The Good
There are many appreciated features in ColdFusion Builder. Having a unified environment for html, cfml, css and JavaScript is wonderful. I'm looking forward to the days when libraries for jQuery and the like are available too. Snippets are something I'm starting to use more regularly, and hopefully with a bit of tweaking before release will be real time savers. One of the best things I can say about it is that it does pretty much everything that my old CFEclipse/Aptana install did, aside from the stuff listed below, but in a more unified way.
Code completion (get in the habit of hitting ctrl-space!!) is something that has really enhanced my productivity. Not just for tag attributes, it works really well on variable names and closing tags. Another nice feature is that it will close any custom tags you add to a page. Put <boo> in your code, type in </ and ctrl-space will offer </boo> back. For XML, as well as for custom tag sets, this is a real time saver.
The Annoying
One issue that drives me batty is it's lack of automated and stable cold folding. When working with cfcs, a page full of unfolded code is a visual nightmare. Having to manually fold the entire page, then unfold all the bits/pieces in the functions I'm working on is a real pain. The fact that code randomly unfolds while you work is also annoying, but that is the type of bug you can expect in a beta product. Hopefully the ability to load cfc's with functions folded is a feature that they will add before final release. (Vote via the links here if you agree).
Another is the lack of HTML shortcuts when working in a CFML document. A big part of ColdFusion is in the view, and it can be tedious to write these parts without quick keys for paragraphs, hrefs, etc. Also, a quick key for <br> would be nice when debugging.
There was an issue with the Java Heap size which triggered during big searches, but this blog post by Marc Esher solved that issue.
The last one is keyboard lag. This is something I've experienced in Eclipse before, so I don't put the blame squarely on CF Builder, but if too many 'helper functions' are trying to parse my every keystroke then there are bound to be some frustrating moments. Cut/Paste seems to be one of the worst culprits, I assume because it triggers a cascade of linking/coloring/syntax-checking/etc. and et.al. functionality.
The Bad
One issue that I've found really frustrating is that, should CF Builder suffer a crash or force shut-down, it refuses to run again. The load screen will appear, vanish, and it's bananas to you. After a thankfully brief bit of experimenting I discovered that deleting the .bolt file fixed the issue.
There have also been some spectacular crashes, the likes of which I haven't seen since the days of Windows 95. Full-on gray screens covering my monitors, then tons of visual artifacts until I can finally kill off the process completely.
The Conclusion
So far it hasn't completely broken my fondness for CFEclpse, and I've admittedly switched back to that IDE until the Java exceptions drive me back. It has a lot of promise though, and like the Flex IDE I'm sure it will solidify and become an even more productive tool in subsequent releases.

Sep 16, 2009 at 3:07 PM The work around I have used for the code folding is to use the outline view, if you go into your eclipse preferences and go to Coldfusion/Editor Profiles/Editor/Outline and just add in what tags you want to be able to skip to quickly this helps.
Sep 16, 2009 at 10:32 PM @Mark thanks for that! I've pulled the Outline window up and it helps a lot.
Dec 20, 2009 at 4:42 PM Deletion of the .bolt file to solve CFBuilder not booting up - you, sir, win at the internet - thank you :)
I've been trying to find an answer to this for ages, and an uninstall/reinstall hadn't worked for some unknown reason.